Realizing 3D Smart Dust ParticlesZeynep Dilli

Introduction & Outline MIT Lincoln Laboratories FDSOI

Process: Adapted to chip stacking 3D Run in April 2005 Outline:

System DescriptionProcess informationPhotodiodes: Design and LayoutSimulation ResultsLayouts

Proposed System 3D system concept: Three tiers

Sensor (Energy harvesting/Photosensor) Storage (Energy) Electronics (Local Oscillator and Output Driver)

Proposed System Submitted proposal for a self-powered local oscillator circuit Area Assigned: 250 microns by 250 microns Total size: 250 x 250 x 800 microns

ip

Process information 0.2 μm, fully

depleted Silicon-on-insulator

Silicon islands 50 nm thick

Three-metal process

Three tiers stacked

Through-vias Top two tiers

turned upside-down

Figure adapted from MIT_LL 3D01 Run Application Notes

Photodiodes: Design Issues Photocurrent=Responsivity [A/W] x Incident Power Responsivity= Quantum efficiency x λ [μm] /1.24

For red light, λ [μm] /1.24 = 0.51 Incident Power = Intensity [W/μm2] x Area [μm2]

Sunlight intensity ≈ 1x10-9 W/μm2

Quantum Efficiency = [# electron-hole pairs]/ [# incident photons]

Depends on reflectance, how many carrier pairs make it to the outer circuit, and absorption

At 633 nm (red light), absorption coef. ≈3.5e-4 1/nm amount of photons absorbed in 50 nm depth is (1-exp(-αd)) ≈ 0.017

η = 0.017 x reflectance x ratio of non-recombined pairs ≈ 0.017 x 0.75=0.013

Photocurrent=0.013 x 0.51 x 1x10-9 x Area[μm2]

= 6.63 pA/μm2

Major problem: The material depth is very small

Photodiodes: Design Issues Photocurrent=0.013 x 0.51 x 1x10-9 x Area[μm2]

= 6.63 pA/μm2

Photosensitive area is pn-junction depletion region width (Wd) times length

Available implants: Body threshold adjustment implants (p-type CBN and n-type CBP, both 5x1017 cm-3); higher-doped source-drain implants and capacitor implants; undoped material is p-type, ~1014 cm-3.

Two diode designs: CBN/CBP diode and pin diode (CBP/intrinsic junction) CBN/CBP diode Wd=0.0684 μm; A=0.5472 μm2

Pin-diode Wd ≈ 1.5 μm; A=15 μm2; possibly problematic Layout: 2062 CBN/CBP diodes: 7.48 nA; 52 pin diodes: 5.17 nA

To increase: Higher-intensity light; optimal wavelength (higher wavelength increases λ/1.24, but decreases absorption)

Expect about 10 nA

Photodiodes: CBN/CBP Diode Layout

Photodiodes: pin diode layout

Operation ip=10 nA, C=30 pF

Operation ip=10 nA, C=30 pF

Operation ip=10 nA, C=30 pF

Operation ip=40 nA, C=30 pF

Layout: Tier 1, Local Oscillator

Layout: Tier 2, CapacitorTop plate: Poly

Bottom plate: N-type capacitor implant, CAPN

Extracted value: 29 pF

Expected value: 30 pF

Layout: Tier 3, Diodes and Pads

“GND” “VDD”

Oscillator output